Traditionally, a typical method of manufacture of plastic tubes uses, for example, injection molding or extrusion molding to mold a tube of the desired diameter and length. However, fiber-reinforced resins that are moldable by these methods can have discontinuous fibers (short fiber lengths), and the product plastic tube suffers from poor strength.
More recent methods of manufacture of plastic tubes use continuous fibers to obtain lighter and stronger plastic tubes. A known typical example of such methods is a method that uses filament winding. FIG. 16 is a diagram representing a manufacturing method based on filament winding.
Referring to FIG. 16, a resin-impregnated fiber base material 51 in a resin tank 50 is wound around a rotating mandrel 53 multiple times through a delivery eye 52, and is cured after a predetermined number of rotations to achieve a tube shape of the desired thickness. A problem, however, is the low productivity and the high cost due to the high investments needed for the equipment, and the need for multiple winding to achieve the desired thickness.
There are methods that address this problem, as in, for example, JP-A-8-72157. FIG. 17 is a diagram representing the sheet winding method described in this publication.
Referring to FIG. 17, a thermoplastic prepreg 41 is shaped into a tube by being wound around a mandrel 31 with a guide 32 disposed between an upper plate 11 and a lower plate 12 constituting rolling plates. In this method, the prepreg 41 disposed on the guide 32 is heated and softened on the side of the lower plate 12 provided with a heating means 23, and wound around the mandrel 31 as the lower plate 12 moves. About halfway through the winding, the prepreg 41 is forcibly cooled with, a cooling means 19 provided on the upper plate 11. After a full rotation, the prepreg 41 is reheated and fused under the heat of the heating means 23 of the lower plate 12. After being wound a predetermined number of times, the prepreg 41 is finally cooled with a second cooling means provided on the lower plate 12.
However, the configuration of the related art requires winding the prepreg 41 a predetermined number of times until the final shape (thickness) is achieved, and repeating the heating and cooling procedures for fusing and solidification. The heating and melting temperature of molding also needs to be set in a temperature range high enough to melt the matrix resin but low enough not to melt the reinforcement fibers. Further, the winding process involves repeated heating and cooling performed roughly for the same duration in the first and the second half of each rotation. It is accordingly difficult to set temperature conditions, and the process involves low productivity and high cost. Another drawback is that a tubular structure produced by the process is often incomplete as a product, and requires a post-process for imparting a functional shape (e.g., a part to toe joined to other tubes), for example, at the ends or the middle of the tube. A problem, however, is that such a functional shape cannot be easily imparted to the plastic tube.